Notify about backup with mail

RUNBOOK.md

@@ -47,6 +47,37 @@ Run once, by hand, on the server:
    # create a remote named "scaleway", type S3, matching your Scaleway
    # Object Storage credentials and region
    ```
+7. Set up email notifications (optional — skip this if you don't want mail):
+   Install a mail transport agent (choose one):
+   ```bash
+   # Option A: mailutils (Debian/Ubuntu) — includes /usr/bin/mail
+   apt install -y mailutils
+
+   # Option B: msmtp + mailutils (lightweight, no full MTA)
+   apt install -y msmtp msmtp-mta mailutils
+   ```
+   Configure the recipient address. Either set `MAIL_TO` in the environment
+   (`/etc/environment` or the cron file itself) or edit `borg-backup.sh`:
+   ```
+   MAIL_TO="${MAIL_TO:-you@example.com}"
+   ```
+   If using `msmtp`, configure `/etc/msmtprc`:
+   ```
+   # /etc/msmtprc — example for Gmail SMTP
+   defaults
+   auth           on
+   tls            on
+   tls_trust_file /etc/ssl/certs/ca-certificates.crt
+
+   account        default
+   host           smtp.gmail.com
+   port           587
+   from           backup-sender@gmail.com
+   user           backup-sender@gmail.com
+   password       your-app-password
+   ```
+   The script auto-detects which command is available (`mail` → `sendmail` → `msmtp`)
+   and falls back silently if none is present — notifications are never fatal.
 
 ## 2. Deploying the Scripts
 
@@ -62,9 +93,9 @@ chmod +x /opt/backup-agent/dump_db.sh
 ## 3. Scheduling
 
 Add a cron entry to run the backup daily, off-peak:
-
 ```
 # /etc/cron.d/borg-backup
+MAIL_TO=you@example.com
 30 2 * * * root /opt/backup-agent/borg-backup.sh >> /var/log/borg/cron.log 2>&1
 ```